1. Field of the Invention
The present invention relates to a calibration mechanism positioned in a scanner, more specifically, to a calibration mechanism capable of alternating the background color and the gray scale and a scanner having the calibration mechanism.
2. The Related Art
In an auto document feeding scanner, a scanning module is fixed for scanning a movable document conveyed by rollers. A calibration sheet positioned to face the scanning module is used to adjust the shade value of the scanning module and to a background. Conventionally, if the scanned document is a light color paper such as a white paper, then the calibration sheet must be manually replaced as a dark color paper such as a black paper. If the scanned document is a dark color paper such as a black paper, then the calibration sheet must be manually replaced as a light color paper such as a white paper.
Therefore, users can enhance the de-skew function and the document edge detection function if the contrast between the scanned document and the calibration sheet is strong enough. Furthermore, the calibration sheet can be manually replaced as a gray sheet for adjusting the shade value of the scanning module.
However, it is inconvenient to manually replace the different calibration sheets and store the different calibration sheets. Moreover, it is easy to contaminate the calibration by human's finger's gripping. The quality of the scanned image, the de-skew function and the document edge detection function will be degraded if the scanning module scans the dirty calibration sheets.